Facetime allows video calls for iOS. Facetime-Audio, added in iOS 7, allows audio only calls. The audio version uses a vulnerable URL scheme which is not used by Facetime Video.
The URL Scheme used for Facetime-Audio allows a website to establish a Facetime-audio call to the attacker's account, revealing the phone number or email address of the user browsing the site.

By entering the URL in an inline frame, the attack is automated, and similar to a CSRF attack across apps. Safari does not prompt the user before establishing the call.

**Impact**

A user browsing the web could click a malicious link or load a page containing a malicious link within an inline frame. The user would then automatically contact the phone number or email address specified in the URL, revealing his identity to the attacker.

**Proof of Concept**

Entering the following URL in iOS would trigger the call to the email address specified: facetime-audio://user (at) host (dot) com [email concealed]

This inline frame would have the user call the specified email address as soon as the HTML page is loaded, without prompting the user: